Appropriate prosthetic care for geriatric patients requires that the needs of the patients, respective activities and medical necessities are addressed. The need for safety is often at the forefront, so that while standing a locking of the knee joint is desired. It is intended that the locking can as far as possible be activated both load-dependently and angle-dependently and induce the feeling of stability in every standing situation, since the coordinating capability, mobility and physical strength of such patients may sometimes be limited.
If the patient is mobile, during walking there should be a high flexion resistance in the standing phase in order to avoid unwanted bending, since bending often cannot be compensated quickly enough by a stretching from the hip.
Sitting on the other hand requires a low resistance, both in the direction of extension and in the direction of flexion, in order that the patient can move unhindered.
It may also be necessary to provide a triggering of the swing phase, in order to make walking more comfortable for the patient.
Artificial joints, in particular knee joints, for ortheses or prostheses have an upper connection part and a lower connection part, which are connected to each other by way of a joint device. In the case of a knee joint, receptacles for an upper leg stump or an upper leg rail are arranged on the upper connection part, while a lower leg shaft or a lower leg rail is arranged on the lower connection part. In the simplest case, the upper connection part and the lower connection part are connected to each other pivotably by a single-axis joint. Only in exceptional cases is such an arrangement sufficient for ensuring the desired success, for example support in the case of the use of an orthesis or a natural gait pattern in the case of use in a prosthesis.
In order to represent as naturally as possible or be conducive to the various requirements during the various phases of a step, or in the case of other tasks, resistance devices which offer a flexion resistance or an extension resistance are provided. The flexion resistance is used to set how easily the lower connection part can be pivoted with respect to the upper connection part in the direction of flexion. In the case of a knee joint, the flexion resistance is therefore used to set how easily the lower leg shaft or the lower leg rail swings backward in relation to the upper leg shaft or the upper leg rail when a force is applied. The extension resistance retards the forward movement of the lower leg shaft or the lower leg rail and may form a stretching stop. In the case of other types of joint, such as the hip joint or the ankle joint, these statements apply in a way corresponding to the kinematic conditions.
It is possible by using settable resistance devices to adapt the respective flexion resistance and extension resistance to the user of the prosthetic or orthotic device or to make allowance for different gait or movement situations, in order to be able to offer an adapted resistance under changing conditions.
DE 10 2008 008 284 A1 discloses an orthopedic knee joint with an upper part and a lower part arranged pivotably thereon and assigned a number of sensors, for example a bending angle sensor, an acceleration sensor, an inclination sensor and/or a force sensor. The extension stop is set in dependence on the sensor data determined.
DE 10 2006 021 802 A1 describes a control of a passive prosthetic knee joint with adjustable damping in the direction of flexion for the adaptation of a prosthetic device with upper connecting means and a connecting element to an artificial foot. The adaptation is for climbing stairs, a low-torque lift of the prosthetic foot being detected and the flexion damping being lowered in a lifting phase to below a level that is suitable for walking on level ground. The flexion damping may be raised in dependence on the changing of the knee angle and in dependence on the axial force acting on the lower leg.
DE 10 2007 053 389 A1 describes a method and a device for controlling an orthopedic joint of a lower extremity with at least one degree of freedom, with an adjustable actuator for adapting to walking situations that differ from walking on level ground an orthopedic device which has upper connecting means to a limb and an orthopedic joint arranged in a jointed manner distally in relation to the connecting means. In this case, a number of parameters of the orthopedic device are detected by way of sensors, the detected parameters are compared with criteria that have been produced on the basis of a number of parameters and/or parameter profiles and stored in a computer unit, and a criterion that is suitable on the basis of the parameters or parameter profiles determined is selected. On the basis of the criterion selected, bending resistances, bending extents, driving forces and/or how they vary over time are set in order to control special functions that deviate from walking on level ground. A tilting angle of part of the orthopedic device in space and/or a variation of a change in tilting angle of part of the orthopedic device may be used as parameters.
Furthermore, the prior art discloses what are known as brake knee joints, in which the flexion resistance and extension resistance are mechanically increased as axial loading becomes greater. This is achieved in the simplest case by providing two braking surfaces which are pressed onto each other by the ground reaction force. Such a configuration cannot be used on the braking device for modern prosthetic knee joints with controlled resistance devices.
It has proven successful for knee joints to offer a high resistance in the standing phase during walking or while standing, the joint not being locked completely. In the case of a fully stretched knee joint, the bending of the joint is prevented by the force vector lying ahead of the joint axis, and consequently the joint being pressed into the stretching stop. As soon as the force vector migrates behind the joint axis, there is the risk of the joint buckling. It is therefore necessary likewise to offer an increased resistance in a slightly bent position. The fact that the joint does not completely lock in a slightly bent position has the advantage that the user of the joint still has possibilities of intervening in the movement of the joint. Should he for example be standing on stairs and lose his balance, a locked joint would cause him to fall in an uncontrolled manner, whereas he can still bend a joint with a high flexion resistance by means of the stump force and thereby mitigate the consequences of falling or prevent falling entirely. Likewise, high damping when standing makes it easier for the joint to be maneuvered in confined spaces or to be set down.
If the joint only offers a high resistance and does not completely lock, it is not possible for example for loading to be applied to the prosthesis when standing on inclined surfaces if the ground reaction force vector migrates too far toward the heel, and consequently no longer lies ahead of the knee axis but behind the knee axis and thereby bends the knee. Standing on a bent knee is also not possible, because the knee bending has the effect that the knee joint axis migrates ahead of the ground reaction force vector and, as a result, the knee is bent further.
Furthermore, the prior art discloses devices in which a separate mode must be set in order to activate locked standing on a ramp or on a bent knee. In such a mode, the joint cannot be bent any further than up to a settable angle. To walk any further or sit down, it is necessary to change deliberately to another mode.